Poly(methyl methacrylate) is a well-known commodity polymer. It has been extensively used in a variety of applications ranging from glass window replacements such as, for example, in the aircraft industry and homes to other uses such as, for example, molded parts in automobiles like instrument cluster lenses, tailgate and parking light lenses, and sidemarker lenses. Because poly(methyl methacrylate) is a brittle material, having a glass transition temperature on the order of about 105.degree. C., many uses for this material in the past have required either the use of plasticizers to make the material more pliable, and moldable, or have required the use of rubber modifiers to toughen the polymethyl methacrylate.
One of the many uses for poly(methyl methacrylate) is molded articles and one of the common techniques for forming such articles is injection molding. Generally, the rubbers that have been used to toughen the poly(methyl methacrylate) are not miscible with the material and, during the injection molding process, form highly visible and weak weld lines because of this immiscibility. Additionally, the molded products formed from rubber toughened polymethyl methacrylate, not infrequently, are characterized by relatively rough surfaces. The rubber toughened polymethyl methacrylates do not have a significantly altered glass transition temperature (T.sub.g); consequently their molding time is relatively long and their molding temperature's high. Such rubber toughened materials are not conveniently used as films because they have high film forming temperatures.
The plasticizers which have been employed with polymethyl methacrylate are the traditional liquid plasticizers. In addition to not significantly altering the glass transition temperature of the poly(methyl methacrylate) these plasticizers unfortunately are relatively volatile. Consequently, depending on the use environment, it is not uncommon for these plasticizers to exude and evaporate from the molded article and unacceptably condense in the adjacent area. This, for example, quite frequently can happen with the plasticizers condensing on the interior windows and parts of an automobile.
Briefly, the essential problem in the past with the use of plasticizers and rubber toughened material is their inability to lower the T.sub.g, their volatility, and immiscibility.
Rubber toughening can be attempted in two ways. First, the polymethyl methacrylate can be toughened by physically blending rubber materials. Another technique is to form a layered polymer by polymerizing methyl methacrylate as an outer layer.
The problems noted above are especially acute with respect to physical blends of polymethyl methacrylate with acrylate rubbers. Of course, those skilled in the art will readily appreciate that it is much more desirable to modify polymethyl methacrylate by the simple expedient of physical blending as opposed to the more complicated necessity of performing a multi-component and/or multi-step chemical reaction to form a different chemical reaction product.
Thus, from the foregoing, it will be seen that there is a need in the art to provide for a physically blended polymethyl methacrylate compound which produces a smoother surface as well as one that upon injection molding will produce a stronger and less visible weld line. Additionally it would be desirable if such polymethyl methacrylate could be modified so that it can be molded faster and at lower temperatures because it also has a lower melt viscosity. Similarly there is a need to provide such a modified polymethyl methacrylate with a lowered glass transition temperature because this will then allow the material to be formed, at lower temperatures, into molded articles for a wide variety of uses, as well as films. Such formulations could then be used, for example, as a silent paint because of the high absorption of acoustical energy. Finally there is a need in the art to provide for a material which can plasticize the polymethyl methacrylate and which is non-volatile.